In Situ Emergency Disposal of Liquid Mercury Leakage by Fe

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In situ emergency disposal of liquid mercury leakage by Fecontaining sphalerite: Performance and reaction mechanism Yong Liao, Yulin Xia, Sijie Zou, Peng Liu, Xiaoliang Liang, and Shijian Yang Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.6b01994 • Publication Date (Web): 12 Dec 2016 Downloaded from http://pubs.acs.org on December 13, 2016

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Industrial & Engineering Chemistry Research

In situ emergency disposal of liquid mercury leakage by Fe-containing sphalerite: Performance and reaction mechanism Yong Liao,┼ Yulin Xia, ╪, § Sijie Zou, ┼ Peng Liu, ╪, § Xiaoliang Liang, ╪, ║ Shijian Yang ┼, ∗ ┼

Jiangsu Key Laboratory of Chemical Pollution Control and Resources Reuse, School of

Environmental and Biological Engineering, Nanjing University of Science and Technology, Nanjing, 210094, P. R. China ╪

CAS Key Laboratory of Mineralogy and Metallogeny, Guangzhou Institute of Geochemistry,

Chinese Academy of Sciences, Guangzhou, 510640, P. R. China §

University of Chinese Academy of Sciences, Beijing, 100049, P. R. China

║

Guangdong Provincial Key Laboratory of Mineral Physics and Materials, Guangzhou, 510640,

P. R. China

∗

Corresponding author phone: 86-18-066068302. E-mail: [email protected] (S. J. Yang). 1

ACS Paragon Plus Environment


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Abstract: The indoor concentration of mercury is often higher than the reference concentration due to the historic accidents with mercury containing devices. Therefore, there is a great demand to develop a treatment for the accidental breakage of the devices containing liquid mercury. In this work, Fe-containing sphalerite was developed as a cost effective sorbent for the in situ emergency disposal of liquid mercury leakage. Fe-containing sphalerite showed an excellent performance for elemental mercury capture at room temperatures with the capacity of much greater than 8.65 mg g-1 and the reaction rate of 4.82 µg g-1 min-1. The formed Hg species on Fe-containing sphalerite was HgS, so it was thermally stable at room temperatures, poor leachable and low toxicity to microorganism. The chemical adsorption of elemental mercury on Fe-containing sphalerite mainly followed the Mars-Maessen mechanism and approximately followed a pseudo-zero order kinetic reaction. The reaction rate of elemental mercury with Fe-containing sphalerite mainly depended on the concentration of Hg0 physically adsorbed on the surface. The physical adsorption of Hg0 on sphalerite was remarkably promoted after the incorporation of Fe, which may be mainly related to the presence of cation vacancies on Fe-containing sphalerite.

Keywords: Fe-containing sphalerite; elemental mercury removal; HgS; in situ emergency disposal; cation vacancy.

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1. Introduction Liquid elemental mercury has the unique physical and chemical properties, so it is widely used in a range of household devices for example body temperature thermometer, fluorescent compact lamp and gas flow meter. These devices containing liquid mercury are unfortunately made of glass and they can be easily broken resulting in a leak of liquid mercury into the residential environment. Although the amount of mercury released from a broken body temperature thermometer (~ 1 g) or a broken compact fluorescent (~ 1 mg) seems negligible for the global emission of mercury, the released elemental mercury will rapidly saturate the air in an enclosed space resulting in a high concentration of elemental mercury in the indoor air. 1 Then, gaseous elemental mercury is largely removed from the air by breathing and approximately 80% of that is taken up by the body. Elemental mercury is readily adsorbed in the respiratory tract and can adversely affect the central nervous system resulting in the symptoms including tremors, increased excitability, and delirium. 2 Therefore, there is a great demand to develop a treatment for the emergency disposal of liquid mercury leakage due to the accidental breakage of the devices containing liquid mercury such as compact fluorescent lamp and body temperature thermometer. 3 Most of the treatments available for the disposal of liquid mercury at ambient temperatures are based on the formation of amalgams, selenides and sulfides. 4-6 Elemental mercury can react with some metals (for example Zn, Cu, Au and Ag) to form a semisolid alloy, which is the so-called amalgamation. 7 As the vapor pressure obtained in the amalgam of cost effective metals (i.e. Cu and Zn) is still high, this technique by itself is insufficient to completely immobilize mercury.5 Recently, Robert et al. reported that nanoscale selenium can be used as a reactive component for the suppression of mercury released from a broken compact fluorescent lamp.

3, 8, 9

However, the cost of selenium

nanoparticles for this particular application is relatively high. Because of the high affinity of mercury with sulfur, the most cost effective treatment for the emergency disposal of liquid mercury leakage is seemingly the conversion of mercury to sulfide. Although the conversion can be achieved by mixing solid sulfur with liquid mercury, the reaction rate is very low at room temperatures resulting in a long time for the disposal. 5

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Although the adsorption of mercuric ions onto metal sulphides has been proposed as an effective method to remove this highly toxic element from aqueous system, 10-14 only the coinage group metal sulfides (for example CuS, Ag2S, Au2S and Au2S3) showed high reaction rates with elemental mercury because their metal cations had strong reduction potentials.

15

However, the

application of these sulfides for the in situ emergency disposal of liquid mercury leakage was extremely restrained due to the high cost. Early transition metal sulfides such as moloybdenite have multiple bonds to sulfur resulting in a less ability for the sulfur to bond with other atoms, so their abilities for elemental mercury capture at room temperatures are poor.

15

The character of

metal-sulfur single bands in the late transition metal sulfides leaves the sulfur with lone electron pairs thus facilitating bonding with mercury,

15

so the late transition metal sulfides may show an

excellent performance for elemental mercury capture. So far, few studies reported that the late transition metal sulfides showed an excellent performance for elemental mercury capture at room temperatures. Therefore, there is a tremendous challenge to improve the performance of late transition metal sulfides for elemental mercury capture at room temperatures. In this work, a novel Fe-containing sphalerite was developed as an efficient sorbent to capture gaseous elemental mercury and stabilize liquid mercury at room temperatures for the in situ emergency disposal of liquid mercury leakage.

2. Experimental 2.1 Preparation of sorbent Zn powder and S powder were both from the Sinopharm Chemical Reagent Co., Ltd. Sphalerite (i.e. ZnS) and Fe-containing sphalerite (i.e. Fe0.1Zn0.9S) were both synthesized using the hydrothermal method. 16-18 Suitable amounts of ferrous chloride and zinc chloride were dissolved in deionized water with the cation concentration of 0.60 mol L-1 and Fe:Zn of 1:9. Meanwhile, suitable amount of sodium sulfide was dissolved in deionized water with S2- concentration of 0.9 mol L-1. 75 mL of the metal cation solution was directly added into 75 mL of the Na2S solution under magnetic stirring. The mixture was then sealed in a Teflon-lined autoclave with the capacity of 200 mL at 160 oC for 24 h. The precipitates were harvested by centrifugation and washed 4 times with deionized water before freeze-drying. Sphalerite was synthesized using the method in 4


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the absence of ferrous chloride. 2.2 Characterization BET surface area was determined by a nitrogen adsorption apparatus (Quantachrome, Autosorb-1). XRD pattern was recorded on an X-ray diffractometer (Bruker-AXS D8 Advance) operating between 20° and 80° at a step of 7° min-1. XRD patterns (including the lattice parameter and crystal size) were analyzed by the software of MDI Jade 5. X-ray photoelectron spectra (XPS) over the spectral regions of Fe 2p, Zn 2p, S 2p, O 1s and Hg 4f binding energies were recorded on an X-ray photoelectron spectroscopy (Thermo, ESCALAB 250) with Al Kα (hv=1486.6 eV) as the excitation source and C 1s line at 284.8 eV as the reference for the binding energy calibration. XPS fitting was optimized without constraints by a sufficient number of Gaussian-Lorentzian curves using the software of XPSPEAK. 2.3 Capture of gaseous elemental mercury Elemental mercury capture was performed on a fixed-bed quartz tube microreactor.

19, 20

The

mass of sorbent with 40-60 mesh was 50-1000 mg, and the reaction temperature ranged from 20 to 50 oC. 200 mL min-1 (room temperature) of the simulated gas contained approximately 1.60 mg m-3 of gaseous elemental mercury (balance of air) was continuously introduced into the reaction tube. The humidity of simulated gas was adjusted to 0-70% using the bubbling method. An elemental mercury permeation tube was used to provide the constant feed of elemental mercury concentration. Gaseous elemental mercury concentration in the inlet or outlet was determined online by a cold vapor atomic absorption spectrophotometer (CVAAS, Lumex R-915+). 2.4 Stabilization of liquid mercury The stabilization of liquid mercury was performed at room temperature (i.e. 17 oC). 0.3 g of liquid mercury was added into a gas-washing bottle and 200 mL min-1 of air was introduced into the bottle. Then, 8 g of Fe-containing sphalerite were added into the bottle with four installments. The concentration of gaseous elemental mercury in the outlet during the process was determined online. 2.5 Safety test To investigate the thermal stability of Hg species on Fe-containing sphalerite, temperature programmed desorption of Hg (Hg-TPD) was carried out on the fixed-bed quartz tube 5



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microreactor with the N2/air gas flow of 700 mL min-1 at a rate of 10 oC min-1 from room temperature to 600 oC. The leachability of mercury from Fe-containing sphalerite after elemental mercury capture was determined using deionized water, saline and toxicity characteristic leaching procedure (TCLP, 5.7 mL L-1 of glacial acetic acid, pH=4.93) as the extraction fluids with the liquid to solid ratio of 20:1. 21 To evaluate the biological toxicity of Hg species on Fe-containing sphalerite, E. coli K-12, which is a representative Gram-negative bacterium, was chosen as the model bacterium for the toxicity test.

19, 22

The toxicity test was carried out at room temperature

under the irradiation of fluorescent tubes in a glass reactor (containing 50 mL of saline solution, 50 mg of Fe-containing sphalerite before and after elemental mercury capture and approximately 1×107 cfu mL-1 of E. coli K-12). 0.1 mL of the sample after the dilution was immediately spread on the nutrient agar plates, and the cell number on the agar plate after the incubation at 37 °C for 24 h was counted.

3. Results and discussion 3.1 Performance of Fe-containing sphalerite for elemental mercury disposal 3.1.1 Capture of gaseous elemental mercury by Fe-containing sphalerite Figure 1a shows the breakthrough curves of gaseous elemental mercury capture by Zn powder, S powder, sphalerite and Fe-containing sphalerite. Zn powder, S powder and sphalerite all showed poor abilities for the capture of a high concentration of gaseous elemental mercury at 20 oC. However, Fe-containing sphalerite showed an excellent ability for gaseous elemental mercury capture at 20 oC, and most of gaseous elemental mercury can be captured by 100 mg of Fe-containing sphalerite. The capacity of Fe-containing sphalerite for gaseous elemental mercury capture was much greater than 8.65 mg g-1 (the breakthrough curve within 60 h test only reached 47%), which was higher than those of S-impregnated activated carbon and nano selenium. 3 More dosage of the sorbent is generally acceptable for the emergency disposal of mercury leakage. Therefore, the parameter of the reaction rate of the sorbent with elemental mercury may be more important than that of the capacity. Figure 1b shows that the reaction rate of Fe-containing sphalerite with elemental mercury at 20 oC reached approximately 4.82 µg g-1 min-1, which was 1-2 orders of magnitude higher than those of S powder, Zn powder and sphalerite (shown in 6


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Figure 1b). Furthermore, the reaction rate of Fe-containing sphalerite with elemental mercury was much higher than those of CuS and Ag2S. 15 3.1.2 Effect of reaction temperature and humidity Figure 2a shows the breakthrough curves of gaseous elemental mercury capture by Fe-containing sphalerite at 20-50 oC. With the increase of reaction temperature from 20 to 50 oC, the reaction rate of gaseous elemental mercury with Fe-containing sphalerite increased. It suggests that the reaction between gaseous elemental mercury and Fe-containing sphalerite was promoted with the increase of reaction temperature. There is usually some H2O vapor in the indoor air, so the effect of humidity on gaseous elemental mercury capture by Fe-containing sphalerite was investigated. Figure 2b shows that elemental mercury capture by Fe-containing sphalerite was slightly restrained with the increase of the humidity from 0 to 50%. With the further increase of the humidity to 70%, elemental mercury capture by Fe-containing sphalerite was remarkably restrained and the reaction rate of gaseous elemental mercury with Fe-containing sphalerite at 20 oC decreased to approximately 1.02 µg g-1 min-1. The inhibition of humidity on elemental mercury capture by Fe-containing sphalerite may be mainly related to the competition of H2O vapor with elemental mercury for the adsorption sites. However, the effect of high humidity on elemental mercury capture by Fe-containing sphalerite can be easily eliminated by increasing the mass of Fe-containing sphalerite. Figure 2b shows that approximately 99% of the removal efficiency of gaseous elemental mercury can still be obtained with 1 g of Fe-containing sphalerite even with the humidity of 70%. 3.1.3 Stabilization of liquid mercury As 200 mL min-1 of air was purged into the bottle containing 0.3 g of liquid mercury, the concentration of gaseous elemental mercury in the outlet reached at a stable level of approximately 1250 µg m-3 and the rate of elemental mercury emission was approximately 0.254 µg min-1 (shown in Figure 3). After 2 g of Fe-containing sphalerite was added into the bottle, the concentration of gaseous elemental mercury in the outlet decreased to approximately 75 µg m-3 and the rate of elemental mercury emission simultaneously decreased to approximately 0.016 µg min-1. With the further addition of Fe-containing sphalerite, the concentration of elemental mercury in the outlet and the rate of elemental mercury emission both further decreased (shown in 7



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Figure 3). As the mass of Fe-containing sphalerite increased to 8 g, little elemental mercury can be observed in the outlet. It suggests that the leaked liquid mercury can be well stabilized by Fe-containing sphalerite. 3.2 Risk assessment of Hg species on Fe-containing sphalerite 3.2.1 Leaching experiment The initial amount of mercury adsorbed on Fe-containing sphalerite was approximately 90 µg. However, mercury in the leachates of deionized water, saline and TCLP were all not detected. It suggests that the leaching of Hg from Fe-containing sphalerite after elemental mercury capture was neglectable. The EPA limitation of Hg concentration in the leachate for classifying a material as hazardous waste is 0.2 mg L-1.

21

Therefore, Fe-containing sphalerite after elemental mercury

capture was not a hazardous waste and it was relatively safe. 3.2.2 Toxicity test Figure 4 shows the inactivation of E. coli K-12 by Fe-containing sphalerite before and after elemental mercury capture. In the presence of Fe-containing sphalerite, no obvious decrease of the bacterial population was observed after 6 h stirring. It suggests that Fe-containing sphalerite did not show an obvious acute toxicity to microorganism. Therefore, the toxicity of Fe-containing sphalerite after elemental mercury capture would be mainly related to Hg species adsorbed if it had the toxicity. 19 Figure 4 shows that the decrease of the bacterial population in the presence of Fe-containing sphalerite after elemental mercury capture still cannot be clearly observed. It suggests that the biological toxicity of Hg species on Fe-containing sphalerite can be approximately neglected. 3.2.3 Thermal stability Figure 5 shows the Hg-TPD profiles of Fe-containing sphalerite after elemental mercury capture under N2 and air atmosphere. Hg-TPD profiles under N2 and air atmosphere both show a desorption peak of Hg0 at approximately 310 oC. Meanwhile, the amount of Hg0 desorbed resulted from the Hg-TPD profiles was close to the amount of Hg adsorbed resulted from the breakthrough curves. It suggests that most of Hg adsorbed on Fe-containing sphalerite can be thermally desorbed as elemental mercury. Figure 5 shows that little Hg0 can be observed below 150 oC in the

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Hg-TPD profiles. It suggests that Hg species adsorbed on Fe-containing sphalerite was relatively thermally stable at ambient temperatures. 3.3 Characterization of Fe-containing sphalerite 3.3.1 XRD and BET surface XRD patterns of synthesized sphalerite and Fe-containing sphalerite were shown in Figure 6. Their characteristic reflections corresponded very well to the standard card of cubic sphalerite (JCPDS: 05-0566). The lattice parameter of synthesized sphalerite was 0.54047 nm. After the addition of Fe, the lattice parameter of Fe-containing sphalerite increased to 0.54088 nm. It suggests that Fe ion was introduced into the structure of cubic sphalerite. 23, 24 The crystal sizes of sphalerite and Fe-containing sphalerite were approximately 11 and 4.2 nm, respectively. Therefore, the BET surface area of sphalerite (48.7 m2 g-1) was much less than that of Fe-containing sphalerite (90.7 m2 g-1).

25

Although the BET surface area of Fe-containing sphalerite was

approximately twice that of sphalerite, the reaction rate of Fe-containing sphalerite with elemental mercury was approximately 26.5 times higher than that of sphalerite. It suggests that increase of BET surface was not the key factor for the promotion of the chemical adsorption of elemental mercury on sphalerite due to the incorporation of Fe. 3.3.2 XPS Figure 7 shows the XPS spectra of sphalerite, Fe-containing sphalerite and Fe-containing sphalerite after elemental mercury capture over the spectral regions of Zn 2p, Fe 2p, S 2p, O 1s and Hg 4f. The Zn 2p 3/2 binding energy of sphalerite mainly appeared at 1021.7 eV (shown in Figure 7b), which was attributed to Zn2+ in ZnS or ZnO. 26 The S 2p binding energies of sphalerite mainly centered at 161.5 and 162.7 eV (shown in Figure 7c), which were assigned to S2- and S22-, respectively.

27, 28

Furthermore, the S 2p binding energies centered at approximately 164, 167 and

169 eV corresponding to S0, SO32- and SO42- cannot be observed on sphalerite.

29

O species on

sphalerite can be clearly observed at 531.9 eV (shown in Figure 7d). The presence of O species on sphalerite suggests that its surface had been oxidized. Furthermore, the absence of SO42- and SO32suggests that the incorporated oxygen was mainly bonded with the metal cations (i.e. Zn). After the incorporation of Fe, no obvious changes appeared on sphalerite over the spectral regions of Zn 2p, S 2p and O 1s (shown in Figure 7). The binding energy of Fe 2p 3/2 on 9



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Fe-containing sphalerite mainly centered at 711.1 eV (shown in Figure 7g), which was attributed to Fe3+.

27

The binding energy at approximately 707 eV corresponding to Fe2+ bonded with S2-

cannot be observed. 28 It suggests that most Fe2+ on Fe-containing sphalerite was oxidized to Fe3+. Sphalerite becomes easier to be oxidized after the incorporation of Fe as the surface of Fe-containing sphalerite is more favorable for O2 adsorption.30 This phenomenon was also demonstrated by the XPS analysis that O concentration on Fe-containing sphalerite (26.5%) was much higher than that on sphalerite (12.3%). After elemental mercury capture, no obvious changes appeared on Fe-containing sphalerite over the spectral regions of Zn 2p, Fe 2p, S 2p and O 1s (shown in Figure 7). The binding energies of Hg species on Fe-containing sphalerite mainly appeared at 100.7 and 104.8 eV (shown in Figure 7n), which was assigned to HgS. 28, 29, 31 HgS is relatively stable and insoluble in H2O and acid, so Fe-containing sphalerite after elemental mercury was poor leachable and low toxicity to microorganism. 3.4 Mechanism of elemental mercury capture by Fe-containing sphalerite The chemical adsorption of elemental mercury on sphalerite and Fe-containing sphalerite can approximately follow the Mars-Maessen mechanism.

6

During the chemical adsorption of

elemental mercury on metal oxides through the Mars-Maessen mechanism, metal cations with strong reduction potentials (for example Mn4+ and V5+) on the surface serve as the oxidant. 25, 32-35 XPS analysis shows that there were Fe3+, Zn2+, O2-, S2- and S22- on Fe-containing sphalerite. Therefore, the potential oxidants were Fe3+ and S22- on Fe-containing sphalerite, and O2 in gas phase. Figure 8 shows that Fe-containing sphalerite showed an excellent performance for Hg0 capture under N2 atmosphere and the presence of O2 did not show an obvious promotion. Meanwhile, XPS analysis demonstrates that the formed Hg species was HgS. Therefore, gaseous O2 was ruled out. Figures 7g and 7k show that Fe species appeared on Fe-containing sphalerite mainly in the form of FeIII-O. Even if physically adsorbed Hg0 can be oxidized by Fe3+, the oxidation of physically adsorbed Hg0 on Fe-containing sphalerite needed to overcome the strong binding energy between Fe3+ and O2-. Therefore, the reaction rate of Hg0 oxidation by FeIII-O on the surface would be very low at low temperatures. Figure 8 demonstrates that FeIII-O on nano maghemite and hematite can hardly oxidize Hg0 physically adsorbed at 30 oC. If physically 10


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adsorbed Hg0 on Fe-containing sphalerite was oxidized by Fe3+ on the surface, the chemical adsorption of Hg0 on Fe-containing sphalerite under air atmosphere would be much better than that under N2 atmosphere due to the regeneration of Fe3+ on the surface by gaseous O2.33 However, the performance of Fe-containing sphalerite for the chemical adsorption of Hg0 under N2 atmosphere was close to that under air atmosphere (shown in Figure 8). Furthermore, the formed Hg species was HgS, which cannot form through the oxidation of physically adsorbed Hg0 by FeIII-O. Therefore, Fe3+ was also ruled out. As a result, the chemical adsorption of elemental mercury on sphalerite and Fe-containing sphalerite mainly involved S22- on the surface and the chemical adsorption can be approximately described as follows: 36

H g 0 (g) +surface → H g 0 (ad)

(1)

H g 0 (ad) + ≡ S 22 − → H gS+ ≡ S 2 −

(2)

According to Reaction 2, the rate of the chemical adsorption of elemental mercury can be approximately described as:

−

d[Hg 0 (g) ] dt

=−

d[Hg 0 (ad) ] dt

= k [Hg 0 (ad) ][S 22 - ]

(3)

Where, k, [Hg0(g)], [Hg0(ad)] and [S22-] were the reaction kinetic constant, the concentration of elemental mercury in gas phase, the concentration of elemental mercury physically adsorbed, and the concentration of S22- on the surface, respectively. The concentration of elemental mercury physically adsorbed on sphalerite and Fe-containing sphalerite was very low, which was many orders of magnitude lower than the concentration of S22on the surface. It suggests that the slight decrease of S22- concentration on the surface due to the reaction with physically adsorbed elemental mercury can be approximately neglected. Therefore, S22- concentration on the surface during the chemical adsorption of elemental mercury can be approximately regarded as a constant. As the concentration of gaseous elemental mercury was relatively high for the surface to be saturated with the physical adsorption of elemental mercury, the concentration of elemental mercury physically adsorbed can be approximately regarded as a constant during the chemical adsorption.33, 35 Hinted by Equation 3, the chemical adsorption of elemental mercury would approximately reach the steady state (shown in Figure 1a), and the rates 11



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of the chemical adsorption of elemental mercury on sphalerite and Fe-containing sphalerite mainly depended on the product of the concentration of S22- on the surface and the concentration of elemental mercury physically adsorbed. XPS analysis shows that the concentration of S22- on Fe-containing sphalerite (11.2%) was close to that on sphalerite (12.1%). However, the rate of the chemical adsorption of Hg0 on Fe-containing sphalerite was approximately 26.5 times than that on sphalerite at 20 oC. Hinted by Equation 3, the concentration of Hg0 physically adsorbed on Fe-containing sphalerite was much high than that on sphalerite. It suggests that the physical adsorption of Hg0 on sphalerite (i.e. Reaction 1) was remarkably promoted after the incorporation of Fe and the promotion of the chemical adsorption of gaseous Hg0 on sphalerite due to Fe incorporation was mainly attributed to the promotion of the physical adsorption of gaseous Hg0. Fe2+ can lost electrons and participate in the oxidation of Fe-containing sphalerite. 30 As Fe2+ in the cubic sphalerite structure was oxidized, cation vacancies would be introduced to maintain the sphalerite structure. 23, 37, 38 Our previous studies on the chemical adsorption of gaseous elemental mercury on Fe-based spinel demonstrated that cation vacancies on the surface were the excellent active sites for the physical adsorption of elemental mercury.25, 33, 34, 39 XPS analysis shows that most of Fe2+ on Fe-containing sphalerite had been oxidized to Fe3+ (shown in Figure 7e). They suggest that there were many cation vacancies on Fe-containing sphalerite. Therefore, the promotion of the physical adsorption of Hg0 on sphalerite due to Fe incorporation may be mainly related to the presence of cation vacancies on Fe-containing sphalerite.

4. Conclusion Fe-containing sphalerite showed an excellent performance for the in situ emergency disposal of liquid mercury leakage. Meanwhile, the formed Hg species on Fe-containing sphalerite was HgS, which was thermally stable at ambient temperatures, poor leachable and low toxicity to microorganism. The rate-determining step of the chemical adsorption of elemental mercury on sphalerite was the physical adsorption of elemental mercury on the surface. The physical adsorption of Hg0 on sphalerite was remarkably promoted after the incorporation of Fe, which may be mainly related to the presence of cation vacancies on Fe-containing sphalerite. 12


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Acknowledgements: This study was financially supported by the National Natural Science Fund of China (Grant No. 21207067 and 41372044) and the Natural Science Fund of Jiangsu Province (Grant No. BK20150036).

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References: (1) Carpi, A.; Chen, Y. F. Gaseous elemental mercury as an indoor air pollutant. Environ. Sci. Technol. 2001, 35, 4170. (2) Landrigan, P. J.; Wright, R. O.; Birnbaum, L. S. Mercury toxicity in children. Science 2013, 342, 1447. (3) Johnson, N. C.; Manchester, S.; Sarin, L.; Gao, Y. M.; Kulaots, I.; Hurt, R. H. Mercury vapor release from broken compact fluorescent lamps and in situ capture by new nanomaterial sorbents. Environ. Sci. Technol. 2008, 42, 5772. (4) Granite, E. J.; Myers, C. R.; King, W. P.; Stanko, D. C.; Pennline, H. W. Sorbents for mercury capture from fuel gas with application to gasification systems. Ind. Eng. Chem. Res. 2006, 45, 4844. (5) Rodriguez, O.; Padilla, I.; Tayibi, H.; Lopez-Delgado, A. Concerns on liquid mercury and mercury-containing wastes: A review of the treatment technologies for the safe storage. J. Environ. Manage. 2012, 101, 197. (6) Granite, E. J.; Pennline, H. W.; Hargis, R. A. Novel sorbents for mercury removal from flue gas. Ind. Eng. Chem. Res. 2000, 39, 1020. (7) Dong, J.; Xu, Z. H.; Kuznicki, S. M. Magnetic multi-functional nano composites for environmental applications. Adv. Funct. Mater. 2009, 19, 1268. (8) Lee, B.; Sarin, L.; Johnson, N. C.; Hurt, R. H. A nano-selenium reactive barrier approach for managing mercury over the Life-cycle of compact fluorescent lamps. Environ. Sci. Technol. 2009, 43, 5915. (9) Ralston, N. Nano-selenium captures mercury. Nat. Nanotechnol. 2008, 3, 527. (10) Jeong, H. Y.; Sun, K.; Hayes, K. F. Microscopic and spectroscopic characterization of Hg(II) immobilization by mackinawite (FeS). Environ. Sci. Technol. 2010, 44, 7476. (11) Xiong, Z.; He, F.; Zhao, D. Y.; Barnett, M. O. Immobilization of mercury in sediment using stabilized iron sulfide nanoparticles. Water. Res. 2009, 43, 5171. (12) Jeong, H. Y.; Klaue, B.; Blum, J. D.; Hayes, K. F. Sorption of mercuric ion by synthetic manocrystalline mackinawite (FeS). Environ. Sci. Technol. 2007, 41, 7699. 14


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(13) Han, D. S.; Orillano, M.; Khodary, A.; Duan, Y. H.; Batchelor, B.; Abdel-Wahab, A. Reactive iron sulfide (FeS)-supported ultrafiltration for removal of mercury (HgII) from water. Water. Res. 2014, 53, 310. (14) Qu, Z.; Yan, L. L.; Li, L.; Xu, J. F.; Liu, M. M.; Li, Z. C.; Yan, N. Q. Ultraeffective ZnS nanocrystals sorbent for mercury(II) removal based on size-dependent cation exchange. ACS Appl. Mater. Interfaces 2014, 6, 18026. (15) Martellaro, P. J.; Moore, G. A.; Peterson, E. S.; Abbott, E. H.; Gorenbain, A. E. Environmental application of mineral sulfides for removal of gas-phase Hg0 and aqueous Hg2+. Sep. Sci. Technol .2001, 36, 1183. (16) Kumar, S.; Verma, N. K. Structural, optical and magnetic investigations on Fe-doped ZnS nanoparticles. J. Mater. Sci.: Mater. Electron. 2015, 26, 2754. (17) Deulkar, S. H.; Bhosale, C. H.; Sharon, M. Optical studies on non-stiochiometric (Zn, Fe)S chalcogenide bulk pellets prepared by coprecipitation. Mater. Chem. Phys. 2008, 111, 260. (18) Nie, E. Y.; Liu, D. L.; Zhang, Y. S.; Bai, X.; Yi, L.; Jin, Y.; Jiao, Z. F.; Sun, X. S. Photoluminescence and magnetic properties of Fe-doped ZnS nano-particles synthesized by chemical co-precipitation. Appl. Surf. Sci. 2011, 257, 8762. (19) Dang, H.; Liao, Y.; Ng, T.; Huang, G.; Xiong, S.; Xiao, X.; Yang, S.; Wong, P. K. The simultaneous centralized control of elemental mercury emission and deep desulfurization from the flue gas using magnetic Mn-Fe spinel as a co-benefit of the wet electrostatic precipitator. Fuel Process. Technol. 2016, 142, 345. (20) Liao, Y.; Xiong, S.; Dang, H.; Xiao, X.; Yang, S.; Wong, P. K., The centralized control of elemental mercury emission from the flue gas by a magnetic rengenerable Fe-Ti-Mn spinel. J. Hazard. Mater. 2015, 299, 740. (21) Bisson, T. M.; Xu, Z. H. Potential hazards of brominated carbon sorbents for mercury emission control. Environ. Sci .Technol. 2015, 49, 2496. (22) Najera, I.; Lin, C. C.; Kohbodi, G. A.; Jay, J. A. Effect of chemical speciation on toxicity of mercury to Escherichia coli biofilms and planktonic cells. Environ. Sci. Technol. 2005, 39, 3116. (23) Lepetit, P.; Bente, K.; Doering, T.; Luckhaus, S. Crystal chemistry of Fe-containing sphalerites. Phys. Chem. Miner. 2003, 30, 185. 15



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(24) Osadchii, E. G.; Gorbaty, Y. E. Raman spectra and unit cell parameters of sphalerite solid solutions (FexZn1-xS). Geochim. Cosmochim. Acta 2010, 74, 568. (25) Yang, S. J.; Guo, Y. F.; Yan, N. Q.; Wu, D. Q.; He, H. P.; Qu, Z.; Jia, J. P. Elemental mercury capture from flue gas by magnetic Mn-Fe spinel: Effect of chemical heterogeneity. Ind. Eng. Chem. Res. 2011, 50, 9650. (26) Gabby, K. L.; Eisele, T. C. Selective removal of mercury using zinc sulfide. Miner. Metall. Process. 2013, 30, 91. (27) Skinner, W. M.; Nesbitt, H. W.; Pratt, A. R. XPS identification of bulk hole defects and itinerant Fe 3d electrons in natural troilite (FeS). Geochim. Cosmochim. Acta 2004, 68, 2259. (28) Behra, P.; Bonnissel-Gissinger, P.; Alnot, M.; Revel, R.; Ehrhardt, J. J. XPS and XAS study of the sorption of HgII onto pyrite. Langmuir 2001, 17, 3970. (29) Saha, A.; Abram, D. N.; Kuhl, K. P.; Paradis, J.; Crawford, J. L.; Sasmaz, E.; Chang, R.; Jaramillo, T. F.; Wilcox, J. An X-ray photoelectron spectroscopy study of surface changes on brominated and sulfur-treated activated carbon sorbents during mercury capture: Performance of pellet versus fiber sorbents. Environ. Sci. Technol.2013, 47, 13695. (30) Chen, J. H.; Chen, Y. A first-principle study of the effect of vacancy defects and impurities on the adsorption of O2 on sphalerite surfaces. Colloid. Surface A: Physicochem. Eng. Asp. 2010, 363, 56. (31) Ehrhardt, J. J.; Behra, P.; Bonnissel-Gissinger, P.; Alnot, M. XPS study of the sorption of Hg(II) onto pyrite FeS2. Surf. Interface. Anal. 2000, 30, 269. (32) Yang, S.; Guo, Y.; Yan, N.; Wu, D.; He, H.; Xie, J.; Qu, Z.; Yang, C.; Jia, J. A novel muti-functional magnetic Fe-Ti-V spinel catalyst for elemental mercury capture and callback from flue gas. Chem. Commun. 2010, 46, 8377. (33) Yang, S.; Guo, Y.; Yan, N.; Wu, D.; He, H.; Xie, J.; Qu, Z.; Jia, J. Remarkable effect of the incorporation of titanium on the catalytic activity and SO2 poisoning resistance of magnetic Mn-Fe spinel for elemental mercury capture. Appl. Catal. B-environ 2011, 101, 698. (34) Yang, S.; Guo, Y.; Yan, N.; Wu, D.; He, H.; Qu, Z.; Yang, C.; Zhou, Q.; Jia, J. Nanosized cation-deficient Fe-Ti spinel: A novel magnetic sorbent for elemental mercury capture from flue gas. ACS Appl. Mater. Interfaces 2011, 3, 209. 16


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(35) Yang, S.; Guo, Y.; Yan, N.; Qu, Z.; Xie, J.; Yang, C.; Jia, J. Capture of gaseous elemental mercury from flue gas using a magnetic and sulfur poisoning resistant sorbent Mn/γ-Fe2O3 at lower temperatures. J. Hazard. Mater. 2011, 186, 508. (36) Liao, Y.; Chen, D.; Zou, S. J.; Xiong, S. C.; Xiao, X.; Dang, H.; Chen, T. H.; Yang, S. J. Recyclable naturally derived magnetic pyrrhotite for elemental mercury recovery from flue gas. Environ. Sci. Technol. 2016, 50, 10562-10569. (37) Wright, K.; Gale, J. D. A first principles study of the distribution of iron in sphalerite. Geochim. Cosmochim. Acta 2010, 74, 3514. (38) Pring, A.; Tarantino, S. C.; Tenailleau, C.; Etschmann, B.; Carpentep, M. A.; Zhang, M.; Lin, Y.; Withers, R. L. The crystal chemistry of Fe-bearing sphalerites: An infrared spectroscopic study. Am. Mineral. 2008, 93, 591. (39) Yang, S.; Yan, N.; Guo, Y.; Wu, D.; He, H.; Qu, Z.; Li, J.; Zhou, Q.; Jia, J. Gaseous elemental mercury capture from flue gas using magnetic nanosized (Fe3-xMnx)1-δO4. Environ. Sci. Technol. 2011, 45, 1540.

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Page 18 of 28

Figure captions Figure 1 (a), Breakthrough curves of elemental mercury capture by S, Zn, sphalerite and Fe-containing sphalerite; (b), Reaction rates of S, Zn, sphalerite and Fe-containing sphalerite with elemental mercury. Reaction conditions: the flow rate=200 mL min-1, reaction temperature=20 oC, and the concentration of gaseous Hg0≈1600 µg m-3. Figure 2 (a), Effect of reaction temperature on elemental mercury capture by Fe-containing sphalerite. Reaction conditions: the mass of Fe-containing sphalerite =50 mg, the flow rate=200 mL min-1, and the concentration of gaseous Hg0≈1600 µg m-3; (b), Effect of humidity on elemental mercury capture by Fe-containing sphalerite. Reaction conditions: the mass of Fe-containing sphalerite=100 mg, the flow rate=200 mL min-1, reaction temperature=20

o

C, and the

concentration of gaseous Hg0≈1600 µg m-3. Figure 3 Performance of Fe-containing sphalerite for the emergency handling of liquid mercury leakage. Reaction conditions: liquid mercury mass=0.3 g, room temperature (17 oC) and the flow rate=200 mL min-1. Figure 4 Inactivation efficiencies of Fe-containing sphalerite and it after elemental mercury capture against E. coli K-12 Figure 5 Hg-TPD profiles of Fe-containing sphalerite after elemental mercury capture under N2 and air atmosphere Figure 6 XRD patterns of synthetic sphalerite and Fe-containing sphalerite Figure 7 XPS spectra of sphalerite, Fe-containing sphalerite and Fe-containing sphalerite after elemental mercury capture over the spectral regions of Zn 2p, Fe 2p, S 2p, O1s and Hg 4f Figure 8 Breakthrough curves of elemental mercury capture by nano maghemite, hematite and Fe-containing sphalerite. Reaction conditions: the flow rate=200 mL min-1, reaction temperature=30 oC, and the concentration of gaseous Hg0≈1500 µg m-3.

18


-1

Reaction rate/µg g min

-1

1600 1200 100 mg of Fe-containing sphalerite 100 mg of sphalerite 200 mg of Zn 500 mg of S

800 400

0

Hg concentration/µg m

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


-3

Page 19 of 28

0

4 3 2 1 0

0

30

60

90

t/min

120

150

180

4.82

5

0.013

0.10

S

Zn

0.175

sphalerite Fe-containing sphalerite

b

a

Figure 1 (a), Breakthrough curves of elemental mercury capture by S, Zn, sphalerite and Fe-containing sphalerite; (b), Reaction rates of S, Zn, sphalerite and Fe-containing sphalerite with elemental mercury. Reaction conditions: the flow rate=200 mL min-1, reaction temperature=20 oC, and the concentration of gaseous Hg0≈1600 µg m-3.

19


1200

o

o

20 C


-3

1600

o

30 C

50 C

800 400

Page 20 of 28

1600 1200 800

without H2O

Humidity=30%

Humidity=50% Humidity=70% Humidity=70% (1 g)

400

0

0


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

-3


0

0

30

60

90

120

150

180

t/min

0

0

30

a

60

90

t/min

120

150

180

b

Figure 2 (a), Effect of reaction temperature on elemental mercury capture by Fe-containing sphalerite. Reaction conditions: the mass of Fe-containing sphalerite =50 mg, the flow rate=200 mL min-1, and the concentration of gaseous Hg0≈1600 µg m-3; (b), Effect of humidity on elemental mercury capture by Fe-containing sphalerite. Reaction conditions: the mass of Fe-containing sphalerite=100 mg, the flow rate=200 mL min-1, reaction temperature=20 concentration of gaseous Hg0≈1600 µg m-3.

20


o

C, and the

Page 21 of 28

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 3 Performance of Fe-containing sphalerite for the emergency handling of liquid mercury leakage. Reaction conditions: liquid mercury mass=0.3 g, room temperature (17 oC) and the flow rate=200 mL min-1

21


Cell density/log10 cfu mL

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

-1


7 6 5 4

Fe-containing sphalerite 0 Fe-containing sphalerite after Hg capture

3 2 1 0

0

1

2

3

t/h

4

5

6

Figure 4 Inactivation efficiencies of Fe-containing sphalerite and it after elemental mercury capture against E. coli K-12

22


Page 22 of 28

8000 under N2 atmosphere under air atmosphere

6000 4000 2000

0


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


-3

Page 23 of 28

0

0

100

200

300

400

o

500

600

Temperature/ C

Figure 5 Hg-TPD profiles of Fe-containing sphalerite after elemental mercury capture under N2 and air atmosphere

23



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

sphalerite

20

30

40

50

2θ/degree

60

70

80

Fe-containing sphalerite

Figure 6 XRD patterns of synthetic sphalerite and Fe-containing sphalerite

24


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Page 25 of 28

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


spalerite

sphalerite

sphalerite

Zn 2p

S 2p

161.5

1021.7 162.7

1200

1000

800

600

400

200

Binding Energy/eV

0

1028

1026

1024

1022

1020

1018

1016

170

168

166

Binding Energy/eV

a

164

b

sphalerite

O 1s

162

160

158

Binding Energy/eV

c

Fe-containing spalerite


Zn 2p

1021.8

531.9

536

534

532

530

528

Binding Energy/eV

1200

1000

800

600

400

200

0

1028

1026

d

1024

e

Fe-containing sphalerite 716.1

S 2p


711.1

724.9

1020

1018

f


Fe 2p

1022

Binding Energy/eV

Binding Energy/eV

O 1s 531.7

161.6 162.8

740

735

730

725

720

715

710

705

170

168

Binding Energy/eV

166

164

162

160

158

536

534

g

532

h

Fe-containing sphalerite 0 after Hg capture

Zn 2p

528

i


Fe 2p 716.1

1021.9

530

Binding Energy/eV

Binding Energy/eV


S 2p

711.1

725.0

161.6 162.8

1028

1026

1024

1022

Binding Energy/eV

j

1020

1018

740

735

730

725

720

715

710

705

Binding Energy/eV

k

25


170

168

166

164

162

Binding Energy/eV

l

160

158


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60



O 1s

531.8

Hg 4f

104.8 100.7

536

534

532

530

528

106

104

102

100

Binding Energy/eV

Binding Energy/eV

m

n

98

Figure 7 XPS spectra of sphalerite, Fe-containing sphalerite and Fe-containing sphalerite after elemental mercury capture over the spectral regions of Zn 2p, Fe 2p, S 2p, O1s and Hg 4f

26


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-3

1600 1200 800

30 mg of Fe-containing sphalerite under N2 30 mg of Fe-containing sphalerite 200 mg of γ-Fe2O3

400

0

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60



Page 27 of 28

200 mg of α-Fe2O3

0

0

30

60

90

t/min

120

150

180

Figure 8 Breakthrough curves of elemental mercury capture by nano maghemite, hematite and Fe-containing sphalerite. Reaction conditions: the flow rate=200 mL min-1, reaction temperature=30 oC, and the concentration of gaseous Hg0≈1500 µg m-3.

27



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Table of Content

28


Page 28 of 28

In Situ Emergency Disposal of Liquid Mercury Leakage by Fe

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